Review of thermo-physical properties, wetting and heat transfer characteristics of nanofluids and their applicability in industrial quench heat treatment.

Ramesh G, Prabhu NK - Nanoscale Res Lett (2011)

Bottom Line:
Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics.Further water-based nanofluids are environment friendly as compared to mineral oil quench media.These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices.

ABSTRACTThe success of quenching process during industrial heat treatment mainly depends on the heat transfer characteristics of the quenching medium. In the case of quenching, the scope for redesigning the system or operational parameters for enhancing the heat transfer is very much limited and the emphasis should be on designing quench media with enhanced heat transfer characteristics. Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics. Further water-based nanofluids are environment friendly as compared to mineral oil quench media. These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices. In this article, thermo-physical properties, wetting and boiling heat transfer characteristics of nanofluids are reviewed and discussed. The unique thermal and heat transfer characteristics of nanofluids would be extremely useful for exploiting them as quench media for industrial heat treatment.

Figure 7: SEM micrographs of (a) top surface of steel after cooling with water, (b) top surface of steel after cooling with nanofluid.

Mentions:
The application of nanofluid in nuclear, rocket, transport and transformer industry is presently well known. It should be noted that there is no metallurgical and mechanical properties change in these applications. However, in quenching heat treatment there is a microstructural change in the component. When steel is quenched from the austentic phase, austenite may transform to ferrite, pearlite, bainite or martensite depending on the cooling rate. Phase transformations in solid state are accompanied by volume variation and transformation plasticity. Large thermal stresses and residual stresses are developed during quenching because of non-uniform cooling of parts and associated heat of metal parts released during the phase transformation. AISI 1070 specimens quenched into the water and water-Al2O3 nanofluid showed a martensitic structure (Figure 6). Finer martensitic structure was observed in 0.01% nanofluid with higher hardness [128]. Chakraborty observed the microstructure of the top surface of the steel after spray quenching with water and Water-TiO2 nanofluids. The cooling rate of the nanofluid was much faster than that of water resulting in ferrite-bainite structure whereas only ferrite was obtained for water quenching (Figure 7) [129]. Recent experiments with Al2O3 nanofluid by Gestwa and Przylecka observed that hardening in nanofluid results in higher impact strength in comparison to the impact strength of the samples hardened in the media without nanoparticles for both the C10 and the 16MnCr5 carburized steel samples. They also observed lowest values of the dimension changes for samples hardened and carburized in 10% polymer water solution with 1% of Al2O3 nanoscale particles [104]. It is evident that by adopting nanofluids as quenching media it is possible to obtain the desired microstructure of components and hence the required mechanical properties.

Figure 7: SEM micrographs of (a) top surface of steel after cooling with water, (b) top surface of steel after cooling with nanofluid.

Mentions:
The application of nanofluid in nuclear, rocket, transport and transformer industry is presently well known. It should be noted that there is no metallurgical and mechanical properties change in these applications. However, in quenching heat treatment there is a microstructural change in the component. When steel is quenched from the austentic phase, austenite may transform to ferrite, pearlite, bainite or martensite depending on the cooling rate. Phase transformations in solid state are accompanied by volume variation and transformation plasticity. Large thermal stresses and residual stresses are developed during quenching because of non-uniform cooling of parts and associated heat of metal parts released during the phase transformation. AISI 1070 specimens quenched into the water and water-Al2O3 nanofluid showed a martensitic structure (Figure 6). Finer martensitic structure was observed in 0.01% nanofluid with higher hardness [128]. Chakraborty observed the microstructure of the top surface of the steel after spray quenching with water and Water-TiO2 nanofluids. The cooling rate of the nanofluid was much faster than that of water resulting in ferrite-bainite structure whereas only ferrite was obtained for water quenching (Figure 7) [129]. Recent experiments with Al2O3 nanofluid by Gestwa and Przylecka observed that hardening in nanofluid results in higher impact strength in comparison to the impact strength of the samples hardened in the media without nanoparticles for both the C10 and the 16MnCr5 carburized steel samples. They also observed lowest values of the dimension changes for samples hardened and carburized in 10% polymer water solution with 1% of Al2O3 nanoscale particles [104]. It is evident that by adopting nanofluids as quenching media it is possible to obtain the desired microstructure of components and hence the required mechanical properties.

Bottom Line:
Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics.Further water-based nanofluids are environment friendly as compared to mineral oil quench media.These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices.

ABSTRACTThe success of quenching process during industrial heat treatment mainly depends on the heat transfer characteristics of the quenching medium. In the case of quenching, the scope for redesigning the system or operational parameters for enhancing the heat transfer is very much limited and the emphasis should be on designing quench media with enhanced heat transfer characteristics. Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics. Further water-based nanofluids are environment friendly as compared to mineral oil quench media. These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices. In this article, thermo-physical properties, wetting and boiling heat transfer characteristics of nanofluids are reviewed and discussed. The unique thermal and heat transfer characteristics of nanofluids would be extremely useful for exploiting them as quench media for industrial heat treatment.